docs: def context_structure(self):
          """
          :return: list of Context objects
              (Contains info about labels and environment variables for each line.)
          """
          instructions = []
          last_context = Context()
          for instr in self.structure:
              instruction_type = instr['instruction']
              if instruction_type == "FROM":  # reset per stage
                  last_context = Context()
  
              context = Context(envs=dict(last_context.envs),
                                labels=dict(last_context.labels))
  
              if instruction_type in ["ENV", "LABEL"]:
                  val = get_key_val_dictionary(instruction_value=instr['value'],
                                               env_replace=self.env_replace,
                                               envs=last_context.envs)
                  context.set_line_value(context_type=instruction_type, value=val)
  
              instructions.append(context)
              last_context = context
          return instructions